In vitro salt tolerant rice plants established by step up treatment with 0.5, 1.0, 1.5 and 2.0 % NaCl at 3-week intervals were examined to determine whether they could grow in potted paddy soil containing 0, 0.55 or 0.75 % NaCl till harvesting. All the control plants were necrotic by the 4th week in the culture. At the 10th week of culture, 100 % of the salt-tolerant plants subjected to 0 or 0.55 % NaCl survived, and 78 % of the plants at 0.75 % NaCl. The Na+ and Cl− contents in the leaves of salt-tolerant plants grown at 0.55 and 0.75 % NaCl were about 4 times of those without NaCl. The ion contents in non-tolerant plants and seedling plants were 10 to 12 times of those in 0 % NaCl treatment. One of the hypotheses to explain the present data is that the in vitro step up salt selection induces the capability to maintain no lethal concentration of NaCl in the leaves.